Worse than Sex Parasite: Sex Parasite with Virus

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A sexually transmitted parasite that's extraordinarily widespread
gets even more dangerous when infected with a virus, researchers
say.

Scientists investigated the sexually transmitted disease
trichomoniasis, which is caused by the parasite
Trichomonas vaginalis, a type of microbe known as a
protozoan. Rather than invade human cells, the parasite latches
onto their surfaces and feeds on them.

Trichomoniasis is more common than all
bacterial sexually transmitted diseases combined, annually
affecting nearly 250 million men and women worldwide. People
infected with the parasite become especially vulnerable to other
sexually transmitted diseases, including HIV, which causes AIDS,
and HPV, which is linked with cervical and prostate cancers. In
addition, complications from trichomoniasis include miscarriage,
preterm delivery, low birth weight and infertility.

"Trichomoniasis is associated with devastating consequences for
women due to inflammation and related risks of reproductive
disease," said researcher Raina Fichorova, a reproductive
immunobiologist at Harvard Medical School and Brigham and Women's
Hospital in Boston.

"Unlike flu viruses, for example, this virus can't spread by
jumping out of the cell into another one," said researcher Max
Nibert at Harvard Medical School. "It just spreads between cells
when they [the hosts] divide or mate."

The virus seems to have no detrimental effect on the parasite,
and the widespread nature of this virus led researchers to
suspect it might actually benefit the parasite in some way. To
learn more, the researchers collected Trichomonas from
infected women and tested how both virus-infected and virus-free
versions of the parasite affected human cells grown in lab
dishes.

Currently, trichomoniasis is most often treated with the
antibiotic
metronidazole. However, when researchers killed
virus-infected Trichomonas with this drug, they found
the dying or injured parasites released viruses that inflamed the
human cells.

The virus does not infect the human cells, but it nevertheless
aggravates the harmful effects of the parasite. These findings
may explain why metronidazole does not prevent the harmful
effects trichomoniasis can have on
women's reproduction, and may actually make things worse — it
forces the parasite to release harmful viruses.

The inflammation also might help explain why the parasite makes
people more vulnerable to other
sexually transmitted diseases (STDs). "The inflammation may
destroy or weaken the barriers that keep other infections out,"
Fichorova said.

Scientists aren't sure whether the virus actually helps the
parasite in some way. "The virus may change the parasite's makeup
— for instance, help generate proteins on the parasite's surface
that may subdue immune response and make the parasite more
acceptable to its host," Fichorova said.

Future research should explore what part of the virus' structure
or life cycle may be most vulnerable to drugs, Fichorova added.
"To treat trichomoniasis safely, we have to not only attack this
parasite, but also its virus at the same time."

The scientists detailed their findings online Nov. 7 in the
journal PLOS ONE.